ES2392509T3 - Method and apparatus for non-invasively measuring hemodynamic parameters using parametric data - Google Patents

Abstract

Apparatus for measuring the pressure in a blood vessel of a living subject, the apparatus comprising a flattening element (402) comprising a sensor (422) adapted to determine the pressure associated with said blood vessel and producing signals related to the same, said flattening element being further configured to apply a level of compression to said blood vessel; and a processor operatively connected to said sensor, said processor being configured to generate an estimate of blood pressure within said vessel based at least in part on said signal and scaling data provided to the processor, said estimate being substantially representative of the actual pressure within said blood vessel, characterized in that the processor is further configured to provide scale adjustment data by selecting appropriate scale adjustment data to apply to said signals, or pressure data derived therefrom, said adjustment data being selected at scale using the body mass index (BMI) of said living subject.

Description

Method and apparatus for non-invasively measuring hemodynamic parameters using parametric data.

Background of the Invention

one.

 Field of the Invention This invention relates generally to methods and apparatus for monitoring parameters associated with the circulatory system of a living subject, and specifically to the non-invasive monitoring of arterial blood pressure.

2.

 Description of related technology Medical science has long sought the precise, continuous, non-invasive measurement of blood pressure. The availability of such measurement techniques would allow the caregiver to continuously monitor the blood pressure of a subject accurately and repeatably without the use of invasive arterial catheters (commonly known as "A tubes") in any of several environments including, for example, operating rooms in which continuous, accurate indications of authentic blood pressure are often essential.

Therefore, several well-known techniques have so far been used to non-invasively monitor the arterial blood pressure waveform of a subject, namely auscultation, oscillometry and tonometry. Both auscultation and oscillometry techniques use a conventional inflatable cuff that blocks the subject's brachial artery. The auscultatory technique determines the systolic and diastolic pressures of the subject by monitoring certain Korotkoff sounds that occur as the cuff slowly deflates. The oscillometric technique, on the other hand, determines these pressures, as well as the average pressure of the subject, measuring actual pressure changes that occur in the cuff as the cuff deflates. Both techniques only determine pressure values intermittently, due to the need to inflate and deflate the cuff alternately, and cannot reproduce the actual blood pressure waveform of the subject. Therefore, using these techniques, continuous, authentic, blood pressure monitoring cannot be achieved.

Occlusive cuff instruments of the class described in summary above have generally been somewhat effective in detecting long-term trends in a subject's blood pressure. However, such instruments have generally been ineffective in detecting short-term blood pressure variations, which are critically important in many medical applications, including surgery. For example, US Patent No. 5,042,496 issued to Sjonell issued on August 27, 1991 and entitled "Method for measuring blood pressure and a blood-pressure measuring device for carrying out the method" and international publication No. WO 95/00074 granted to Akinyemi, et al, entitled "Blood Pressure Measuring Apparatus" and published on January 5, 1995, which each discloses a sleeve and monometer assembly of this type.

The technique of arterial tonometry is also well known in medical techniques, see for example WO 01/00087. According to the theory of arterial tonometry, the pressure in a superficial artery with sufficient bone support, such as the radial artery, can be accurately recorded during a flattening scan when the transmural pressure is equal to zero. The term "flattening" refers to the process of varying the pressure applied to the artery. A flattening sweep refers to a period of time during which the pressure on the artery is varied from overcompression to undercompression or vice versa. At the beginning of a decreasing flattening sweep, the artery is overcompressed in a "dog bone" form, so that no pressure pulses are recorded. At the end of the scan, the artery is undercompressed, so that minimum amplitude pressure pulses are recorded. Within the scan, it is assumed that a flattening occurs during which the tension of the arterial wall is parallel to the surface of the tonometer. In this case, the blood pressure is perpendicular to the surface and is the only voltage detected by the tonometer sensor. At this pressure, it is assumed that the peak to maximum peak amplitude pressure ("maximum pulsatile") obtained corresponds to a null transmural pressure.

A prior art device for implementing the tonometry technique includes a rigid arrangement of miniature pressure transducers that is applied against the tissue that lines a peripheral artery, for example, the radial artery. Transducers can each directly detect the mechanical forces in the underlying tissue of the subject, and each is sized to cover only a fraction of the underlying artery. The arrangement is propelled against the tissue, to flatten the underlying artery and thus cause pressure variations between beats within the artery to be coupled through the tissue to at least some of the transducers. A different transducer arrangement is used to ensure that at least one transducer is always on the artery, regardless of the position of the arrangement on the subject. However, this type of tonometer is subject to several drawbacks. First, the network of differentiated transducers is generally not anatomically compatible with the continuous contours of the tissue of the subject lining the artery being detected. This has historically led to inaccuracies in the resulting transducer signals. In addition, in some cases, this incompatibility can cause tissue damage and nerve damage and may limit blood flow to the distal tissue.

Tonometry systems are also commonly quite sensitive to the orientation of the pressure transducer on the subject being monitored. Specifically, such systems show a degradation in accuracy when the angular relationship between the transducer and the artery is varied from an "optimal" angle of incidence. This is an important consideration, since it is not likely that two measures have the device placed or maintained at exactly the same angle to the artery. Many of the previous approaches have similar disadvantages because they cannot maintain a constant angular relationship with the artery regardless of lateral position, due in many cases to placement mechanisms that are not adapted to take into account the anatomical characteristics of the subject, such as the curvature of the wrist surface.

Another significant drawback of arterial tonometry systems in general is their inability to continuously monitor and adjust the level of compression of the arterial wall to an optimal level. Generally, only the optimization of the compression of the arterial wall has been achieved by periodic recalibration. This has required an interruption of the subject's monitoring function, which can sometimes occur during critical periods. This disability severely limits the acceptance of tonometers in the clinical setting.

One of the most significant limitations of the tonometry approaches of the prior art concerns the transfer of incomplete pressure pulse from the inside of the blood vessel to the point of measurement on the skin surface above the blood vessel. Specifically, even when the optimum level of arterial compression is reached, there is an incomplete and often complex coupling of arterial blood pressure through the vessel wall and through the tissue to the skin surface, such that the magnitude Pressure variations that actually occur within the blood vessel is somewhat different from that measured by a tometric sensor (pressure transducer) placed on the skin. Therefore, any waveform or pressure signal measured on the skin necessarily differs from the authentic pressure within the artery. Modeling the physical response of the arterial wall, tissue, muscles, tendons, bone, wrist skin is not a simple task, and inherently includes uncertainties and anomalies for each individual separated. These uncertainties and anomalies introduce an unpredictable error in any measurement of blood pressure made using a tometric sensor. Figures 1 and 2 illustrate the cross section of a typical human wrist, illustrating the various components and their relationships during normal (uncompressed) and flattened (compressed) states.

Figure 3 graphically illustrates the above principles, specifically the variability in the tometric measurements relative to the invasive "tube A" or the authentic blood pressure. Figure 3 shows pulse pressure data (ie, less diastolic systolic pressure) by way of example obtained during flattening of the radial artery of the subject with respect to the mean pressure. Figure 3 demonstrates the differences between the pulse pressures measured with the non-invasive prior art tonic apparatus and the invasive tube A catheter; Note that these differences are generally neither constant nor related to actual pulse pressure. Therefore, there can often be a very significant variance in the measurements derived in a tonic way with respect to the invasive catheter pressure, such variance not being adequately treated by prior art techniques.

Based on the above, an improved methodology and apparatus is needed to accurately measure, continuously and non-invasively, blood pressure within a living subject. Such improved methodology and apparatus will ideally allow a continuous tometric measurement of blood pressure that reflects authentic intraarterial pressure (catheter), while also providing robustness and repeatability under varying patient environment and physiology conditions. Such a method and apparatus will also be easily used by both trained medical personnel and untrained individuals, thus allowing certain subjects to perform self-monitoring accurately and reliably.

Summary of the Invention The present invention satisfies the aforementioned needs by an improved method and apparatus for non-invasively and continuously assessing hemodynamic properties, including arterial blood pressure, within a living subject as defined by the independent claims.

Brief description of the drawings

Figure 1 is a cross-sectional diagram of the wrist area of a human subject by way of

example, which illustrates the radial artery and other tissues and structures, in an unflattened (uncompressed) state.

Figure 2 is a cross-sectional diagram of the wrist area of Figure 1, illustrating the effect

of tonic flattening on structures and radial artery.

Figure 3 is a graph illustrating the relationship between the pulse pressure obtained in a tonic way and the

corresponding invasive catheter (tube A) pulse pressure for a typical human subject when the artery

Radial is flattened to mean blood pressure.

Figure 4 is a side elevational view of an embodiment of the flattening apparatus of the present

invention.

Figure 4a is a plan view of the contact pad of the apparatus of Figure 4, illustrating the relationship between the flattening element and the pressure transducer. Figure 4b is a side cross-sectional view of a second embodiment of the pad of contact, which illustrates the use of multiple layers of material. Figure 4c is a bottom plan view of a third embodiment of the contact pad, which illustrates the use of materials that vary as a function of the radius from the central flattening element. Figure 4d is a side plan view of a fourth embodiment of the contact pad of the invention, which illustrates the use of variable pad material thicknesses. Figures 4e-4f are plan views from below and side, respectively, of a fifth embodiment of the contact pad of the invention. Figures 4g-4h are plan views from below and side, respectively, of a sixth embodiment of the contact pad of the invention. Fig. 5 is a logical flow chart illustrating an exemplary embodiment of the general method. of blood pressure measurement using flattening and scaling optimized according to the invention. Figure 5a is a logical flow diagram illustrating a method of scaling a waveform. tometric range not adjusted to scale using body mass index and pulse pressure. Figure 5b is a graph illustrating a plurality of useful alternative flattening sweeping profiles. with the present invention. Figure 5c is a graph showing an exemplary method of identifying and removing a noise artifact of a tonic pressure waveform using an external signal. Figure 5d is a logical flow chart illustrating an exemplary embodiment of the method of scale adjustment of hemodynamic measurements (using BMI and PP) according to the invention. Figure 5e is a graph showing the relationship between BMI / PP and the error factor for radial artery data. derived from a sample of human beings. Figure 5f is a graph showing the relationship between real and uncorrected tonic systolic pressure for the sample of figure 5e. Figure 5g is a graph showing the relationship between real and uncorrected tonic diastolic pressure for the sample of figure 5f. Figure 5h is a graph showing a waveform of “zero mean” tonic pressure as a example before and after correcting (adjust to scale). Fig. 5i is a logical flow chart illustrating a second exemplary embodiment of the method. for scaling hemodynamic measurements (using BMI and CM) according to the invention. Figure 6 is a graphic representation of a first embodiment of a nomogram useful for adjusting to scale blood pressure measurements according to the methodology of figure 5h. Figure 7 is a logic flow diagram illustrating an exemplary method for laterally positioning the flattening apparatus of figure 4 according to the invention. Figures 7a-7b are graphs illustrating the pulse pressure (PP) versus the lateral position for the first and second lateral position scans of the method of Figure 7, including the relative location of the maximum of PP in them. Figure 7c is a graph of PP versus the lateral position illustrating a parasitic artifact (pressure peak) due to the movement of the subject during the measurement. Figure 7d is a PP plot against the lateral position illustrating a PP profile that does not have a maximum Sure. Fig. 8 is a block diagram of an exemplary embodiment of the measuring device. hemodynamic parameters within the blood vessel of a living subject according to the invention. Figure 8a is a side plan view of a unit transducer / device assembly exemplary storage useful with the apparatus of figure 8. Fig. 9 is a logical flow diagram illustrating an exemplary embodiment of the method of provide treatment to a subject using the methods mentioned above.

Detailed description of the invention Reference is now made to the drawings in which equal numbers refer to equal parts.

It is noted that although the invention is described herein primarily as regards a method and apparatus for evaluating hemodynamic parameters of the circulatory system through the radial artery (i.e., the wrist) of a human subject, the invention can also be carried out. or easily adapt to monitor such parameters in other blood vessels and locations in the human body, as well as to monitor these parameters in other warm-blooded species. All such adaptations and alternative embodiments are easily implemented by those of ordinary skill in the relevant techniques, and are considered to be within the scope of the claims appended hereto.

As used herein, the term "hemodynamic parameter" is intended to include parameters associated with the subject's circulatory system, including for example pressure (for example, diastolic, systolic, pulse or mean pressure). The term "physiological parameter" is intended to include measures or amounts associated with the physiology of the subject, including for example weight, height, body mass index (BMI), wrist circumference, ankle circumference or content in body fat of the subject, but may also include one or more "hemodynamic" parameters previously defined herein (eg, blood pressure, etc.).

Additionally, it is noted that the terms "tometric", "tonometer" and "tonometry" as used herein are broadly referred to the non-invasive surface measurement of one or more hemodynamic parameters such as pressure , such as placing a sensor in communication with the skin surface, although contact with the skin is not required to be direct (for example, such as through a coupling means or other contact surface).

The terms "flatten" and "flattening" as used herein refer to the compression (with respect to a non-compression state) of tissue, blood vessel (s) and other structures such as tendon or subject physiology muscle. Similarly, a "sweep" of flattening refers to one or more periods of time during which the level of flattening is varied (either increasing, or decreasing, or any combination thereof). Although generally used in the context of linear position variations (constant velocity), the term "flattening" as used herein may possibly take any variety of other forms, including without limitation (i) increasing or decreasing compression. nonlinear continuum (for example, logarithmic) over time; (ii) a linear or nonlinear compression not continuous or continuous by segments; (iii) alternating compression and relaxation; (iv) sine wave functions

or triangular; (v) random movement (such as a "random path"); or (vi) a deterministic profile. All such forms are considered to be encompassed by the term.

Finally, it is intended that the terms "processor" and "digital processor" include any integrated circuit or other electronic device (or collection of devices) that can perform an operation on at least one instruction including, without limitation, set core processors reduced instruction (RISC) such as those manufactured by ARM Limited of Cambridge, RU, CISC microprocessors, central processing units (CPUs) and digital signal processors (DSP). The hardware of such devices can be integrated into a single substrate (eg, "matrix" of silicon), or distributed between two or more substrates. In addition, various functional aspects of the processor can only be implemented as software or firmware associated with the processor.

General view

In a fundamental aspect, the present invention comprises a method for accurately measuring one or more hemodynamic parameters using optimal flattening and scaling of unprocessed or non-scale measurements. In general terms, such flattening relieves the loss of transfer and other errors introduced by non-invasive measurement techniques (for example, tometric) applied to the complex system of blood vessels, tissue, muscle and skin, at the measurement location of the hemodynamic parameter. For example, as will be described in more detail below, the present invention is useful for accurately measuring blood pressure using a tometric or surface pressure sensor disposed on the radial artery of a human being, possibly varying the waveform of pressure measured with respect to that actually experienced within the radial artery itself. In one embodiment, a specially configured flattening (compression) apparatus is disclosed, in which a flattening element is used to compress or deflect the tissue and consequently, the blood vessel contained therein. This flattening apparatus advantageously with associated pressure transducer can be used only as described in detail herein, or together with literally any other type of apparatus adapted for measuring hemodynamic parameters, including for example the devices described in the application. US patent in process together with this US 2002055680 entitled "Method and Apparatus for the Noninvasive Assessment of Hemodynamic Parameters Including Blood Vessel Location" filed on March 22, 2001, and US 2002062086 entitled "Method and Apparatus for Assessing Hemodynamic Parameters within the Circulatory System of a Living Subject ”also filed on March 22, 2001, both of which are assigned to the assignee of this document.

In one aspect, application US 2002062086 mentioned above describes a method that generally comprises the steps of: measuring a first parameter of a subject's blood vessel; measure a second blood vessel parameter; derive a calibration function based on the second parameter; and correct the first parameter using the derived calibration function. Once calibrated, the second parameter is monitored continuously or periodically; Changes in that parameter are used to indicate changes in the hemodynamic property of interest. In an exemplary embodiment, the first parameter comprises a pressure waveform, and the second parameter comprises the kinetic energy of total blood flow within the blood vessel. During the measurement of the pressure waveform, the blood vessel is flattened (compressed) to induce changes in hemodynamic properties within the blood vessel and the circulatory system; the kinetic energy and / or velocity is then measured during such flattening and is used to identify one or more artifacts (such as for example a "protrusion" in the kinetic energy profile or velocity). A correction function is then generated based on those artifacts, and is applied to the measured pressure waveform to generate a corrected or calibrated waveform representative of the actual pressure within the blood vessel. In an exemplary embodiment, the calibration method comprises measuring the pressure waveform of a subject's blood vessel; measure a second parameter of the same blood vessel at least once; identify at least one artifact within the pressure waveform based on the second parameter; derive a calibration function based on the second measured parameter and at least one property associated with the at least one artifact; apply the calibration function at least once to the pressure waveform to generate a calibrated representation of the pressure inside the blood vessel; and continuously monitor the second parameter to identify variations in blood pressure over time.

Since the signal being measured (for example the pressure) varies over time, iteration and optimization are selectively used within the algorithm that performs the methodology of the present invention to compensate for this variation. Specifically, the signal varies with time throughout the short period of the cardiac cycle, throughout the longest period of the respiratory cycle and possibly throughout the even longer or shorter period of hemodynamic changes resulting from varying drug concentrations. and volume changes. Therefore, the algorithm described herein uses the flattening mechanism mentioned above to continuously find and maintain the optimum level of flattening, thus maintaining an environment conducive to a precise, continuous and non-invasive parametric measurement.

It will be further noted that the optimal deviation technique of the present invention can be used in conjunction with lateral (transverse), proximal or other placement techniques to help position the pressure transducer (s) on the blood vessel of interest. To do this, any of several different placement approaches can be used either alone or in combination (when compatible). For example, lateral placement may be used based on the analysis of the pressure signal obtained by a tometric sensor generally disposed on the blood vessel (described hereinafter). Alternatively, the mainly acoustic lateral placement and wall detection approaches described in the applications being processed together with the one mentioned above can be used. As yet another alternative, the location and manual placement of the flatteners and the transducer on the selected blood vessel can be employed.

Flattening device for pressure measurement

Referring now to Figures 4-4a, a first embodiment of the flattening apparatus of the invention is described in detail.

The ability to accurately measure the pressure associated with a blood vessel depends largely on the mechanical configuration of the flattening mechanism. In the typical prior art approaches discussed above, the pressure transducer comprises the flattening mechanism such that the mechanism and the transducer are fixed in a single unit. Therefore, the pressure transducer experiences the full force applied to deform the tissue, structures and blood vessel. This approach does not take into account the component of the flattening force required to compress this interposed tissue, etc. since it refers to the pressure measured in a tonic way of the blood vessel. On the contrary, without compression, the magnitude of the pressure inside the blood vessel is attenuated or masked by the tissue interposed in such a way that the pressure measured in a tonic way is less than what actually exists in the vessel (called “transfer loss ").

Instead, the apparatus of the present invention performs the pressure transducer disposed within a flattening element, the latter having a specially designed configuration adapted to alleviate the effects of such transfer loss in a simple, repeatable and reliable manner, in such a way. way that can either be (i) ignored,

or (ii) be compensated as part of the tometric measurement. As discussed in greater detail below, the shape, size, placement and selection of materials for the flattening element may be important in determining the amount of transfer loss experienced in a given set of conditions. Specifically, these factors largely dictate the relationship between the maximum pulse pressure and the average pressure, and therefore ultimately the error associated with a given tometric pressure reading.

As shown in the exemplary embodiment of Figure 4, the flattening element 402 is used to compress the tissue that generally surrounds the blood vessel 404 of interest, and to apply force to the wall of the blood vessel so that the wall or circular tension of the wall begins to be exceeded. The flattening element 402 (or flattener) is coupled to a drive motor 406 that provides compressive flattening force 408 in reaction to the patient through a wrist strap or wristband 410 (or an external surface). The flattener 402 of the illustrated embodiment includes a generally rectangular flattener body 414 with a substantially cylindrical projection 412 (see Figure 4a), and a contact pad 441 disposed on the lower surface thereof. The body 414 is modeled from a polymer (for example, polycarbonate) for its ease of manufacture, rigidity and low cost, although other materials can be chosen. A substantially cylindrical opening 415 is formed in the center of the contact pad 441 to accommodate the projection 412 of the body. Therefore, when the contact surface 440 of the flattener pad 441 is pressed against the patient's skin, a generally rectangular contact zone ("fingerprint") with a central opening is obtained.

A pressure transducer 422, substantially disposed on the blood vessel 404 and housed within an opening 413 of the flattener body 414, is used to obtain tonic pressure readings of the skin (tissue) surface that lines the blood vessel. The height of the active face 420 of the transducer 422 is fixed within its housing 417 to provide the desired degree of coupling between the transducer face and the tissue when the flattener 402 is compressed on the subject's tissue. However, it will be recognized that the transducer 422 or its housing 417 can be manufactured in an adjustable or mobile manner within the opening 413 so that optimal placement in different operating conditions is facilitated and / or adapted to different subject physiology.

As shown in Figure 4, a thin polymer layer 423 is also applied over the top of the transducer face 420 to (i) couple the transducer face more positively to the tissue; and (ii) level the surface that comes into contact with the tissue formed by the transducer face, the projection 412 of the body, and the housing 417 of the transducer. Specifically, a layer of a compressible, flexible silicone-based compound (for example, silicone rubber) is formed on the transducer face 420 within the housing 417 as shown, although other materials may be used. In addition to its superior physical properties and excellent coupling of tissue pressure signal to the transducer face 420, the silicone layer 423 also allows some degree of variation in the distance between the transducer face and the upper surface 419 of the housing 417 during manufacturing, since the silicone "fills" to the proper depth to provide an effectively continuous level and top surface.

The engine 406 of the flattener assembly, in the present embodiment, is rigidly coupled to the wrist assembly 410 to provide a substantially invariable platform against which the motor can exert reaction force while flattening the subject's tissue. This "rigid" configuration is used to avoid any significant elasticity of the assembly as the engine 406 drives the compression pad 441 of the tissue / blood vessel during flattening. This rigidity is advantageous from the point of view that it helps allow the pressure transducer 422 to record the maximum value of the pulse pressure (or other selected parameter); Higher degrees of elasticity in the mechanism tend to reduce the magnitude of the observed peak pressure, thus possibly making the identification of the pulse pressure peak more difficult.

However, it will be recognized that alternative configurations that have at least some degree of elasticity can be used in some applications. For example, in an alternative embodiment, a rigid coupling of the flattener assembly to the bracelet 410 is used; however, a somewhat flexible flattener body 414 with a curved inner surface (not shown) that can be adapted to the curvature of the subject's wrist can be used. In this way, the coupling remains rigid, but the flattener body adapts in a limited manner to the curvature of the subject's wrist, thus allowing a substantially uniform level of contact along a wider part of the wrist. The degree of elasticity of the body 414 is controlled by its flexural strength; that is, the level of force necessary to incrementally deform the body increases as a function of its elasticity or "curvature", thus effectively limiting its total elasticity, and causing the contact pad 441 coupled thereto is preferably compressed after a certain degree occurs. deformation Other alternatives easily designed by the usual experts can also be used.

Advantageously, any of several different wristband configurations compatible with the present invention can be used. For example, the bracelet disclosed in the US patent application being processed together with the present of the assignee US 2002055680 can be used. Other configurations can also be replaced with equal satisfaction, such configurations being easily designed by those skilled in the art.

This prior flexibility in the wristband configuration also emphasizes another benefit of the present invention, specifically that the aforementioned flattening mechanism (and the associated technique described in detail below) is somewhat less sensitive to variations in the position of the flattener and the transducer of pressure with respect to the subject's skin surface than the apparatus and prior art techniques. This lack of relative sensitivity is due in part to the fact that the pressure is coupled through the tissue and the wall of the blood vessel over a fairly wide range of arc with respect to the longitudinal axis of the blood vessel, so that a poor angular alignment (i.e. pressure transducer incidence angles that move away from a normal vector to the skin surface at the measurement point) has less effect. In addition, since the first flattening element 402 comes into contact with a wide area of tissue around the blood vessel and compresses / distorts it to some degree, some poor angular alignment or rotation of the contact surface 440 of the contact element can be tolerated. flattening with respect to the surface of the skin.

The contact pad 441 of the flattening element 402 is formed in the present embodiment by a flexible, compressible foam cell urethane material marketed by Rogers corporation as Poron ™, although other materials with similar qualities may be used together with it, or in instead of, Poron disclosed in this document. Poron has, among other properties, a desirable durometer characteristic that is well adapted for the present application. Contact pad 441 is manufactured approximately 0.25 inches (6.35 mm) thick, although other thicknesses can be used. The assignee of the present document has observed during various field tests that the Poron material provides excellent physical properties with respect to the compression of the subject's blood vessel and tissue, thus alleviating very effectively the aforementioned transfer losses associated with these structures. Additionally, the contact pad 441 of the present embodiment is manufactured so that it can be replaced by the user / subject so that maintenance of a hygienic (or even sterile) environment is allowed. For example, pad 441 can be replaced for each use, together with replacement of the pressure transducer assembly, or for each different subject if desired. The use of a low cost polymer advantageously makes the maintenance cost of the device quite low.

It will be further appreciated that although the contact pad 441 described above and shown in Figure 4a is manufactured of both substantially constant thickness and uniform material composition, any of these parameters can be varied for specific applications. For example, pad 441 can be constructed using a multilayer or "interleaved" approach, the physical properties of the various layers being varied so that certain properties are provided for the overall pad assembly. In one embodiment, a two layer pad (Figure 4h) is used which has different compression constants for each layer to provide a progressively variable compression of the pad; for example, a layer of material will preferably be compressed first, followed by the second layer when the incremental compression force of the first layer exceeds that of the second layer. In another embodiment, the material properties are varied in a generally radial direction with respect to the central opening to provide variable compression rates as a function of the radius from the point of contact with the tissue that lines the blood vessel (Figure 4c). In yet another embodiment (Figure 4d), the thickness of the pad is varied as a function of spatial position to provide varying rates of tissue compression.

Based on the foregoing, it will be appreciated that the configuration of pad 441 can be "fine tuned" as needed to achieve specific tissue compression rates and / or provide other desired performance attributes. The design and manufacture of such alternative embodiments are well known to those of ordinary skill in mechanical and material techniques, and therefore are not further described herein.

Additionally, although the embodiments of Figures 4-4d comprise a substantially flat, rectangular pad 441 with an opening located in the center having a circular cross section, it will be recognized that other shapes and / or configurations can be used. For example, as shown in the embodiment of Figures 4e-4f, the pad 451 of the flattening element comprises a circular cross-sectional shape with a slight concave arc formed on the contact surface 450 such that the pad is adapts to the inner surface of the wrist 455. As yet another alternative (figures 4g-4h), the flattening element pad can be configured as a set of 460 differentiated lateral pads arranged on each side of an arrangement 463 of multiple transducer elements 464 pressure. A myriad of other combinations of shapes, sizes, footprints, flatnesses and configurations of flatteners compatible with the present invention can be used, all such combinations being within the scope of the claims appended hereto.

The motors 406 used in the illustrated embodiment of FIG. 4 to drive the flattening element 402 are a precision "stepper" motor of the type known in motor techniques. This motor also includes one or more position encoders (not shown) that provide an electrical signal to the central system processor and an associated algorithm to control very precisely the position of the flattening element during operation. Therefore, as described in greater detail below, the variable used in the present embodiment to represent the position of the flattening element is the number of motor steps (positive or negative with respect to a "zero" point); This approach advantageously eliminates the need to measure the absolute position with respect to the tissue or the anatomy of the subject. Instead, the relative number of steps is measured by the position encoder, and this correlates effectively with the pressure measurement obtained from the pressure transducer (s).

With respect to Figure 7 below, a detailed assessment of the electronic and signal processing apparatus used to support the operation of the flattening mechanism 400 of the figure is provided.

Four.

Methodology

Referring now to Figure 5, the general methodology of optimally flattening or compressing the blood vessel and local tissue using the apparatus described above is described in detail.

As previously mentioned, a fundamental concept of the present invention (and therefore the methodology presented below) is to control the flattening element 402 in such a way that the loss of transfer associated with the tissue and the structures surrounding the tissue is relieved. blood vessel during measurement. In the case of the human radial artery, the loss of transfer is effectively relieved at the level of flattening at which the pulse pressure measured in a tometric manner is maximized. Too little compression, and the coupling between the blood vessel wall and the tissue surface (and therefore the active surface of the transducer) is incomplete, providing tonic pressure values that are significantly erroneous. Too much compression, and the vessel wall collapses, thus significantly altering the cross-sectional shape of the vessel, and again producing high levels of error. The optimal condition is to attach the vessel wall through the tissue interposed as completely as possible without otherwise affecting the hemodynamics of the vessel itself.

As shown in Figure 5, the first step 502 of method 500 comprises placing the flattening mechanism 400 in position with respect to the subject's blood vessel. Such placement can be achieved manually, that is, by the caregiver or the subject by visually aligning the transducer and the device on the inside of the wrist, by the pressure / electronic / acoustic positioning methods referred to above, or by still other means. Ideally, the flattening element 402 and its contact pad will be conveniently positioned transversely on the inside of the wrist, with the transducer element 422 directly covering the radial artery with little or no inclination with respect thereto. Element 402 and transducer 422 can be aligned laterally (step 504) and aligned proximally (step 506) if required. In an exemplary embodiment, the pressure signal measured in a tonic way obtained from transducer 422 can be used as the basis for such lateral / proximal placement, in a manner similar to that used to determine the optimum level of flattening (described in detail a continuation).

Once the flattening element 402 is properly positioned and oriented, the element 402 is operated according to step 508 to flatten the surrounding tissue (and at least partially cover) the blood vessel to a desired level to identify a position optimal in which the effects of transfer loss and other errors associated with tometric measurement are relieved. Specifically, as shown in the embodiment of Figure 5a, a flattening sweep (step 530) is started using the motor 406 that drives the element 402, thereby gradually increasing the pressure applied to the tissue by means of the contact pad 441. During this scan, the pressure waveform obtained from the transducer 422 is analyzed by intervals (eg, by beats) according to step 532 to determine the pulse pressure value for that interval. Such calculations are generally achieved within a short duration (largely due to the signal processing apparatus described below with respect to Figure 7) with respect to the rate of flattening change such that the necessary calculations can be performed " on the fly ”during the flattening scan. Certain artifacts or conditions that exist within the waveform are identified (step 534), thus indicating that the desired level of flattening has been reached. For example, in the embodiment of Figure 5a, the pulse pressures for each contiguous heartbeat interval are calculated. Amplitude values of "peak to valley" of the waveform are determined for each interval as part of this calculation in the present embodiment, although other quantities and / or parts of the waveform may be used. When the calculated pulse pressure decreases below a certain percentage (for example, 50%) of a previous beat during a designated number of beats (for example, two), a "maximum" of pulse pressure is declared, and the level of flattening is reduced back to that corresponding to the previous heartbeat interval in which the pulse pressure was maximized (step 510 of Figure 5).

The approximate positioning of the flattening element 402 back to the maximum pulse pressure position is achieved in one embodiment using the motor position recorded during the flattening scan (for example, at a given number of motor stages corresponding to the level of flattening or arterial compression in which the maximum pulse pressure was detected). Once the approximate position has been obtained and the flattener has returned to this position, then the system is allowed to “establish” for a period of time, and an iterative “search” approach is used to vary the engine position. and the flattening element in each direction; that is, more flattening and less flattening, while monitoring the average pressure as determined from the pressure transducer 422 (and supporting circuitry). A "maximum" detection routine is used as part of this iterative movement to verify that the maximum point has indeed been achieved and, if required, move the flattening element to that point from the current position. It is noted that although the position of the motor or similar marks corresponding to the maximum pulse pressure are generally a good "approximate" determining factor, other factors (physiological and otherwise) may cause the optimum level of flattening to vary somewhat, therefore needing the maximum detection routine referred to above to obtain the best results. However, depending on the level of accuracy desired, the "approximate" relocation criteria alone can be used if desired.

It will be recognized that a variety of different flattening sweeping profiles can be employed as part of the previous steps. Specifically, the simplest profile is probably the straight linear rate scan, in which the drive motor 406 of the flattening element is controlled by the system controller (described below) to move the flattening element at an effectively constant rate. (for example, 5000 engine steps / min.). This produces a non-linear application of force or deflection in the tissue that is being compressed, since more force will be required to compress the tissue as it approaches full compression as opposed to the onset of flattening. As another alternative, the flattening scan can be gradual linear; that is to say, a contiguous set of constant rate mini-sweeps interrupted by limited pautilization periods without movement. This approach can be useful when significant signal processing or other data processing / acquisition is required during the flattening scan.

As yet another alternative, the flattening rate can be made deterministic. For example, in an alternative embodiment, the rate is coupled to the patient's heart rate, which is determined either directly by the hemodynamic measurement system (i.e., it is extracted from the pressure waveform measured by the transducer 422 of pressure by signal processing), or by another device (such as an electrocardiographic device adapted to analyze the QRS complexes of the heart). Specifically, in an embodiment that uses intrinsic determination by the measured pressure waveform, the extracted heart rate is entered into a linear equation of the form y = mx + b, such that for a high subject heart rate, the flattening rate is set proportionately high, and vice versa. However, it is clear that if desired, nonlinear functions can be substituted. Figure 5b graphically illustrates several of the above alternatives.

Additionally, deterministic amounts may be used as the basis for the determination of the flattening rate. For example, systolic and / or diastolic blood pressure values (or derivations thereof) can be used as inputs for the flattening rate equation. A myriad of other variants, either alone or in combination, can also be used to best select the appropriate flattening rate under variable subject physiological conditions.

Next, according to step 512 of method 500 of Figure 5, the desired pressure value (s) is measured and stored in the system storage device, discussed below. , while the flattening is set at (or servo controlled around) the point at which the pulse pressure is maximized. For example, in one embodiment, the systolic and diastolic waveforms of the signal emitted by the pressure transducer are extracted. It is observed that in the case of the human radial artery by way of example, the flattening point at which the maximum pulse pressure occurs is strongly correlated with the mean arterial blood pressure, the degree of correlation being affected to some degree by the shape, size, footprint, elasticity and other properties of the contact pad 441 previously described herein with respect to Figure 4.

Then, in step 514, they are optionally scaled or the measured values of the hemodynamic values (for example, pressure) are corrected to compensate for the transfer loss as appropriate. It will be recognized that all measured values will not need to be scaled, and in some cases no scale adjustment will be required. This result arises from the fact that (i) different individuals have different physiological characteristics and construction, thus allowing the loss of transfer associated with one individual to be markedly different from that of another; and (ii) the magnitude of the transfer loss (and therefore the error in the tometric measurement compared to the actual intravascular pressure) can be small so that it has no consequences. As will be described in a subsequent assessment herein, there is a strong correlation between the magnitude of the transfer loss for a given individual and their body mass index (BMI), thus allowing the present invention, among other things, scale "intelligently" the hemodynamic parameters measured without processing.

It is noted that the present invention may also use the heart rate signal provided by the aforementioned ECG or other external device as a synchronization signal to help identify artifacts or other characteristics in the pressure waveform obtained in a tonic manner. Specifically, since the non-intrinsic ECG measurement technique (or other) used may not be prone to non-physiological noise (eg, patient movement, vibration of the treatment facility, low frequency AC noise, etc.) , artifacts present in the pressure waveform can be mapped against the external signal for the purpose of correlating and eliminating such artifacts. For example, as is well known, the ECG technique mentioned above uses electrical signals referring to the QRS complex of the subject's heart to measure heart rate; therefore the ECG waveform will record QRS complexes in the interval in which they are generated by the heart of the subject, largely regardless of motion artifact or other noise. Therefore, when the tonic pressure waveform presents a motion artifact (such as someone who administers treatment inadvertently strikes the stretcher on which the subject rests, or the ambulance in which the subject travels crosses a section of bumpy road ) to some extent, such artifacts will generally be absent from the ECG signal. The present invention optionally maps the two coincident signals in the temporal dimension using the digital processor described below with respect to Figure 7, and examines the signals at a predetermined rate and interval (for example, a window of 100 ms of movement every 100 ms),

or after the occurrence of a predetermined event (for example, ECG QRS amplitude that exceeds a given threshold) to determine whether a transient pressure value observed in the data collected for that period should be included, or discarded as a motion artifact or transient value of parasitic noise. In an exemplary embodiment (Figure 5c), the ECG waveform is monitored for the detection of each heartbeat; a window function f (t) is applied to the waveform data obtained in a tonic way to effectively block transient pressure values that occur outside the specified time window, which focuses on the "beat" detected by ECG. Therefore, only artifacts that match heartbeats detected by the ECG will be included in the subsequent signal processing of the tonic waveform. Assuming a random distribution of noise / artifact, the vast majority of such noise / artifact will be removed from the pressure waveform using such a technique.

However, it will be appreciated that other functions and approaches can be used to correlate the external signal (ECG or otherwise) and the waveform. For example, instead of a window approach that has two distinct states (i.e. discard or discard), more sophisticated filtering and signal processing algorithms adapted to selectively identify noise / artifact and eliminate it from the waveform can be used "on the progress". Such algorithms are well known to those of ordinary skill in signal processing techniques, and therefore are not further described herein.

BMI / Pulse pressure (PP) scale adjustment Referring now to Figures 5d-5h, an exemplary embodiment of the methodology for scaling or correcting unprocessed or unadjusted hemodynamic data obtained using the methodology of Figure 5 described above. It will be recognized that although the embodiment of Figures 5d-5h is described in terms of an algorithm as will be used in conjunction with a digital computer system that has a microprocessor or signal processor, the method of the present invention can be practiced in a manner partially or even totally independent of such algorithm or computer system. For example, parts of the algorithm can be achieved by hardware (such as logic circuit performed in ASIC or FPGA), or even manually by direct or indirect operator control. Therefore, the example in Figures 5d-5h is simply illustrative of the broader concepts.

As illustrated in Figure 5d, the scale adjustment method 514 generally comprises first determining a first physiological parameter of the living subject under evaluation (step 540). For the sake of illustration, method 514 is described as to the scaling of a blood pressure measurement obtained in a tonic way from the radial artery of a human being, although it will be appreciated that the method can be used in other monitoring locations in the Same or different species. The first parameter obtained in this exemplary embodiment comprises a body mass index (BMI) of the type well known in medical techniques. Specifically, the BMI includes:

BMI = W / H2 (Ec. 1)

where:

BMI = body mass index (Kg / m2) W = subject weight (kgf) H = subject height (m)

Typical BMI values for the human species range between approximately 15 Kg / m2 and approximately 50 Kg / m2, although values outside this range may occur. The weight (W) and height (H) of the subject are easily obtained using conventional measurement techniques not further described herein. document.

Next, a second physiological parameter of the same subject is determined in step 542. In the embodiment from the method of figures 5d-5h, the pulse pressure is used (i.e. systolic pressure minus pressure diastolic) along with the subject's body mass index (BMI) to generate a corrected pulse pressure.

Figure 5e illustrates the relationship (based on empirical data derived by the assignee of this document, discussed in greater detail below) between the BMI ratio with respect to the measured pulse pressure (PP) tonomically and the error factor (percentage error between the pressure reading derived in a manner tometric and actual intravascular pressure determined by an invasive tube A catheter. As it shown in figure 5e, the relationship between error and BMI / PP is grouped well and is substantially linear for the data presented, covering the latter a wide range of BMI / PP values.

Figure 5e is significant from the point of view that it provides a description of the error behavior as a function of certain selected physiological parameters (for example, BMI and PP). This description allows the present invention to apply the appropriate level of scale adjustment to pressure measurements tometric to correct for the loss of transfer and related errors present in these measures. Such As shown in Figure 5e, losses (as reflected by the error factor) at low BMI / PP values they are low, and increase (linearly) as the BMI / PP increases. In practical terms, people with high BMI for the same PP value will require more correction of transfer loss, which follows from Intuitive way of observing that such people commonly have a greater mass of tissue (skin, fat, muscle, tendon, etc.) interposed between the radial artery and the surface of the skin inside the wrist. For him on the contrary, a very tall, thin person with an average PP value will require little correction for the loss of transfer, which is also intuitively compelling.

Figures 5f and 5g illustrate the relationship between actual intravascular pressure (as measured, for example, by a tube A) and the pressure measured tonomically for systolic and diastolic pressures, respectively, for the data Empirical ones referred to above. As shown in each of these figures, the data They are closely grouped along a functional line (in this case, modeled as linear). Said of otherwise, there are predictable functional relationships between systolic and diastolic pressures measured in a manner tometric and their corresponding real intravascular values.

In the present embodiment, a linear relationship is also used to model the error in percentage between the

actual tonic and intravascular pressures, as follows:

b PP IMCM · PP -PPPP% error TT RT

(Ec. 2)

where:

PPT = pulse pressure (tometric)

PPR = pulse pressure (real)

M = pending

b = intersection

Manipulating this equation, you get the following:

PPT –PPR = M · BMI + b · PPT

(Ec. 3)

PPT –b · PPT - M · BMI = PPR

(Ec. 4)

Y

PPT (1 - b) - M · BMI = PPR

(Ec. 5)

Equation 5 is the generalized relationship regarding real intravascular pressure (PPR) and tometric pressure (PPT) based on BMI. Note that the PPT (also called corrected pulse pressure, PPc) is based on the current interval (eg, heartbeat), while the PPT is based on an average pulse pressure along "n" previous pulses. In this case, "n" can be any number (for example, 10), or become deterministic such as based on another measured amount of the subject or otherwise derived in the calculation process if desired. Therefore, in effect, the PPC / PPT ratio is the scale factor that is applied to subsequent samples of the pressure waveform obtained in a tonic way. A mobile window of “n” intervals is established, in which the same scale factor is applied in each interval (beat).

Despite the use of a linear relationship in equation 5 above (and the functions of Figures 5f and 5g), it will be appreciated that the relationship between BMI / PP and the error factor (or indeed any other physiological parameter or function of the same used for scaling) does not need to be linear or take any recommended form. For example, data collected from the entire population or subsets thereof (for example, those within a specific BMI range) may be decidedly nonlinear. In addition, other parametric relationships such as the BMI / CM approach described above may provide a nonlinear function, which can be used as the basis for scaling. Alternatively, the function can be continuous by segments or even discontinuous. Therefore, a myriad of functional relationships can be successfully substituted and used in a manner compatible with the general premise of the present invention.

Returning to Fig. 5d, the corrected pressure waveform (adjusted to scale) is then derived according to step 544. In the present embodiment, this is determined by (i) subtracting the average pressure measured in a tonic way from "n "Average pulses of each subsequent tometric sample pressure value (a" zero mean "sample result) according to step 546; (ii) multiply each “zero average” sample value derived in (i) by the derived scale factor (step 548), and add again the average average pressure value of “n” beats (step 550); and (iii) repeat the process every “n” beats, using a newly derived scale factor for each “n” beats (step 552). The resulting waveform is a scaled waveform that is effectively corrected for transfer loss.

Note that the previous "zero mean" approach is used to zero or center the waveform around a known reference level (zero). In this way, the systolic pressure measurements will advantageously always be higher than the zero mean, and the diastolic pressure measurements will always be lower. However, if desired, a nonzero average (i.e. deviation) or other reference point can be chosen, such as any value between zero and the measured pressure average. The null-media approach is simply a timely agreement to simplify the analysis and make the results more intuitive for the user / operator. It will be appreciated that such value (s) can be chosen to facilitate calculation efficiency, especially in more "reduced" hardware environments where the computing capacity of the host platform is minimal or scarce. For example, a low cost (or even disposable) apparatus that performs the present invention may have a digital processor with MIPS and / or very limited memory; the midpoint or deviation can therefore be chosen to best optimize this limited capacity.

It is also noted that the magnitude of error associated with the tometric measurements described herein is always negative (Figure 5d is completely on the "negative" side of the error factor scale). This correlates with the tonic pressure always being lower than the actual intravascular pressure in terms of magnitude due to loss of transfer. When this fact is coupled with the “null average” technique described above, it results in tonic systolic and diastolic pressure values that must always be increased in magnitude during scale adjustment (“stretch up” for systolic, and "stretch down," as shown in Figure 5h). As described in greater detail below with respect to Figure 7, the apparatus 700 of the present invention calculates a "stretch" value based on the BMI and PP according to the methodology discussed above that performs this stretching of the shape of tonic wave to meet the actual intravascular waveform.

The use of pulse pressure (PP) as a physiological parameter in the present embodiment provides the additional advantage of being derived from other variables measured by the pressure transducer. That is, PP is derived by mathematical manipulation of systolic and diastolic pressure values at any given time (or over a predetermined interval); therefore, in the exemplary embodiment of the invention in which the determination of the scaling factor is performed algorithmically using pressure values intrinsically obtained by the system during pressure measurement, there is no need that the caregiver or the subject measures such a parameter. This advantageously simplifies the scaling procedure.

As noted above, the data presented above were obtained by the assignee performing clinical trials in the validation of the methodology of the present invention. Specifically, the applicant selected a number (> 20) of random individuals, and obtained multiple waveforms for each. This generated more than 500 data files concerning these individuals. Each data file was divided into a plurality of "iterations" (eg, increments of 10 beats), with the average pressure value calculated over each iteration. The above-mentioned BMI-based scale adjustment was applied to each iteration with a calculated average, collectively analyzing ultimately all scaled-up iterations to generate specific “global” or non-individual data. The radial artery of one arm of each individual was arbitrarily chosen as the basis for the measurements, while the other arm of the same individual (s) was used to provide blood pressure measurements of tube A invasive catheter substantially simultaneous. The results of these "preliminary findings" tests provided very low errors in both systolic and diastolic measurements of approximately -1.2 mmHg (standard deviation = 8.6) and -2.6 mmHg (standard deviation of 5.4) , respectively, after adjusting to scale compared to the corresponding tube A values, thus validating the methodology experimentally. Note that based on the required performance level of +/- 5 mmHg (standard deviation = 8 mmHg) of the well-known AAMI SP10 standard referring to auscultation / oscillometric blood pressure measurement techniques, the clinical performance of the present invention is Excellent.

BMI / CM scale adjustment Referring now to Figure 5i, a second exemplary embodiment of the scale adjustment method is described (step 514 of Figure 5d). In this second embodiment, the second physiological parameter comprises the circumference of the subject's wrist (CM) at the measurement point. This is functionally related to the BMI described above to produce a scale adjustment index, as described in more detail below. In the first step 562 of the scale adjustment method 560 of Figure 5i, the BMI value for the subject is obtained as described hereinbefore with reference to Figure 5d. Next, in step 564, the BMI value determined in step 562 is related to the second parameter (for example, wrist circumference of the same subject) to obtain a scale adjustment index Is as defined in the equation 6:

Is = BMI / CM (Ec. 6)

where:

Is = scale adjustment factor (considered dimensionless) BMI = body mass index (Kg / m2) CM = wrist circumference (cm)

The "typical" values for Is range between approximately 2 and 10, although values outside this can be observed interval. However, note that the term "typical" in this case refers to values observed throughout a wide section of the general population, and variations in body type, bone size, weight, Body fat content and the like can cause significant variations of Is between two individuals.

From the value of the scale adjustment index Is determined for each individual, a Ks scale factor (step 566). Table 1 below illustrates an exemplary approach used for derive the scale adjustment factor Ks from the scale adjustment index Is. This table is derived from empirical data obtained by the assignee during clinical trials of a statistically significant number of individuals, in comparison with auscultation / oscillometry measurements (“cuff”) obtained from the same individuals.

Table 1

Scale Index (Is)

Scale factor (Ks) Observations

> 4.0

1.2 (20%) Significant fatty tissue present in the radial artery

3.3 -4.0

1.09 (9%) Some fatty tissue present in the radial artery

<3.3

1.0 (no scale adjustment) Little fatty tissue present in the radial artery

The realization of table 1 has the advantage of simplifying the process of determining Ks, since the value of Ks to be applied to the measured blood pressure of the subject is chosen from a limited number of differentiated intervals (i.e., intervals of value of Is). For example, a subject is considered to have a value of Is of 2.8. Using Table 1, it can be seen that no adjustment to scale of the unprocessed blood pressure measurement is required. This mainly refers to the subject who has a comparatively large wrist circumference in relation to his BMI, which often indicates the absence of significant amounts of fatty tissue at the measurement site (i.e. radial artery). Less fatty tissue provides a “coupling”

10 more complete (less loss of transfer) between the pressure transducer and the blood vessel wall, thus requiring less adjustment on a corrective scale.

Instead, an individual with an Is value of 6.0 is considered. For this individual, table 1 indicates that a scale factor Ks of 1.2 should be applied (which effectively corrects the pressure value observed upwards by 20

15 percent) Such adjustment to scale is needed because the loss of transfer for this individual is substantially greater, as reflected in the higher ratio of his body mass index (BMI) with respect to his wrist circumference. Therefore, the BMI (numerator) tends to imply or be directly related to the amount of fatty tissue present in the subject's wrist.

Finally, in step 568, the scale factor Ks is applied to the measurement of unprocessed or uncorrected blood pressure to obtain a scale-adjusted or corrected measurement. This is achieved in the illustrated embodiment by simply multiplying the uncorrected pressure measurement by the scale factor Ks. For example, a value not adjusted to a scale of 100 mmHg and a Ks of 1.2 will result in a corrected pressure value of 120 mmHg. As indicated above with respect to the performance of BMI / PP described above, the measured value of

In a tonic way, it will always be lower than the true intravascular pressure, and therefore the tonic value will always be scaled up in terms of magnitude.

It will be recognized that although the realization of Table I above is provided as regards a small number (three) of differentiated scale index intervals, other numbers of intervals (whether equal to 30 magnitude or not, or compressed) may be used. -expansion) to confer a greater degree of precision or granularity to the correction procedure by adjustment to pressure scale. For example, ten (10) intervals arranged in a logarithmic relationship can be used. As yet another alternative, other parameters can be used to qualify or substantiate the scaling procedure. For example, after determining the scale adjustment factor Ks using table 1 (or similar), the proposed scale adjustment factor can be verified against a database

35 statistics for other individuals or subclasses of individuals (for example, those with a BMI greater than a certain value). In this way, aberrant data can be identified before applying the scale adjustment, possibly prompting the caregiver to obtain a confirmation measure or to consult other sources.

Note that since the method of Figure 5i is, at least in the present embodiment, somewhat heuristic, a

40 very accurate measurement of this second parameter is not critical. Therefore, the precise location of the measurement on the subject's wrist is also not critical. This highlights a significant advantage of the present methodology, because the resulting scale adjustment applied to the non-scale pressure measurement is substantially insensitive to errors in the wrist circumference measurements of the physician or caregiver. This advantage also exists with respect to the BMI determination of step 1002 described above, since the

The determination of BMI is quite insensitive to errors in measuring the height and / or weight of the subject.

Alternatively, other physiological parameters can be used to "scale" the waveform (or Ks scale adjustment factor before being applied to the unprocessed pressure measurement). For example, it is well known that the electrical impedance of a subject's tissue in a given region of the body may be related to the subject's body mass. Normally, such measurements are made using electrical signals at high frequencies (for example, 100-200 kHz) to overcome noise and other harmful effects present at lower frequencies. Therefore, the present invention can use an electrical impedance measurement of this type obtained from the wrist

or the subject's arm as the basis for determining body mass (or a parameter equivalent to BMI), the latter being used to scale the tonic pressure waveform. Such measurements can also

55 used with a confirmatory ability to qualify the scale factor derived by other means, and / or provide additional granularity within a given differentiated range of scale factor.

In another embodiment, the relationship between the scale factor Ks and the scale index Is is determined using a nomogram as illustrated in Figure 6. As shown in Figure 6, the nomogram 600 comprises a series of scales 602 , 604, 606, 608, 610, 612, 614 verticals that are arranged in parallel relationship with each other on a flat surface (for example, laminated card, paper or the like), not shown. In the illustrated embodiment, the vertical scales comprise a weight scale 602, a height scale 604, a BMI scale 606, a wrist circumference scale (CM) 608, a scale index scale 610 (Is), a 612 scale of blood pressure measured (unprocessed), and a 614 scale of actual or scale-adjusted blood pressure. The various scales are aligned to allow the sequential determination of the parameters of interest regarding the blood pressure determination methodology adjusted to the scale described above. For example, the two scales 602, 604 are entered to the left (using the data obtained from the subject) and, using a straight edge such as a ruler, the BMI value is determined by aligning the straight edge so that it cuts the scales 602, 604 weight and height in the values obtained from the subject for each. The BMI value is then read from the third scale 606 (BMI) where the straight edge cuts to that scale 606. The construction of such name scales is well known in mathematical techniques, and therefore is not further described in the present document

In the nomogram 600 of Figure 6, the remaining scales (CM, scale factor, measured blood pressure and corrected blood pressure) adjacent to the weight, height and BMI scales are arranged to facilitate the calculation of the corrected blood pressure . Specifically, after calculating the BMI as described above, the user simply places the straight edge on the nomogram such that the edge cuts the BMI 606, 608 and CM scales at the determined BMI value and the CM value. real of the subject, respectively. Then it is determined that the scale factor Ks is the point of intersection of the edge and the scale factor scale 610. Continuing in a similar manner, the user then subsequently aligns the straight edge in such a way that he cuts the unprocessed blood pressure scale and scales 610, 612, thereby cutting the corrected pressure scale 614 at the authentic blood pressure value. (corrected) Using such scales in the same nomogram 600, the present invention allows the user to "move" the straight edge through the nomogram 600, thus avoiding the need to record or even remember the results of intermediate calculations. Specifically, for example, after calculating the BMI, the user simply pivots the straight edge around the intersection point of the straight edge and the BMI scale 606 until the CM scale 608 is properly cut, thereby providing the scale factor. Similarly, the user then pivots the straight edge around the point of intersection of the edge and the scale factor scale 610, and so on. Therefore, the user never needs to even know the BMI or scale factor values determined in these intermediate stages; instead, you only need to remember (or record) the corrected blood pressure value of the last 614 scale. However, optionally a table 625 is provided to record the intermediate values (and initial data obtained from the subject) to facilitate the records calculation and maintenance. With respect to the latter, the nomogram 600 can be reproduced on a sheet of paper that is arranged on a flat surface. The caregiver simply obtains the weight, height and CM data of the subject, enters them in the applicable space in table 625, and then can easily refer to the data when making the nomination determinations mentioned above. After making these determinations, the caregiver records the results in the appropriate spaces of table 625, and then saves the entire sheet in the subject's file or other location. In this way, the determination of blood pressure can be reconstructed advantageously at a later date, thus providing identification of errors and responsibility.

It will be appreciated that the above nomogram 600 of Figure 6 can also be converted to, or reduced to, a "wheel" calculator configuration of the type well known in the art (not shown). Such a wheel comprises a

or more stationary and mobile wheels, normally made of a flexible laminated material, which rotate around a central axis. The periphery or surfaces of the wheels are coded in such a way that when various parts of the wheel are aligned (representing various values of the parameters mentioned above), the resulting value can be read directly from another part of a wheel. Such devices have the advantage of not requiring the use of a flat surface, thus allowing (i) significant mobility to the user, and (ii) preventing the lack of a flat surface or a straight edge from potentially altering the calculation results. Other configurations compatible with the invention can also be used.

It will be further appreciated that the scales of the nomogram 600 as described above can be performed of a differentiated or continuous nature, in a manner compatible with the desired application of the scaling factors. Therefore, the functionality represented in Table 1 above can easily be performed in a nominated way, or alternatively, a continuous, undifferentiated representation can be performed with equal ease (i.e., Is and Ks are continuous variables).

Finally, it is noted that the homologous technique described above can also be applied if desired to the IMC / PP method described above, reducing the calculations of equations 1-5 prior to a nomographic representation by a person skilled in mathematical techniques.

In yet another embodiment of the method of Figure 5i, the relationship between the scale factor Ks and the scale index Is is determined algorithmically by means of a code embedded within the processor or storage device of the blood pressure measuring apparatus ( for example, see the valuation referring to figure 7 below). For example, the relationships in Table 1 above can easily be reduced to an algorithm.

or computer program (such as an assembly language program compiled from a C code list using an assembler) that performs the above-mentioned determinations by the digital processor. A query table or similar structure can also be encoded within the algorithm if desired. This algorithmic embodiment has the distinctive advantage of avoiding the aforementioned nomogram or similar device, and making the blood pressure correction process transparent to the user. Once properly qualified, the use of software code also reduces the risk of error in the determination of scale adjustment, since no misalignment of the straight edge or similar error can occur. The coding and implementation of such an algorithm is easily achieved by those of ordinary skill in computer programming techniques, and therefore is not further described herein.

The results of the various intermediate stages (i.e., determination of BMI, scale factor) can also optionally be presented in any display device associated with the system, and stored within the storage device or other desired location (or transmitted to a remote location such as through a computer network) to facilitate additional analysis.

It will be further recognized that IMC / PP and IMC / CM methodologies can be combined and / or used in a confirmatory manner to complement each other. For example, the scale adjustment factor (and / or corrected blood pressure) determined using the CM-based technique mentioned above can be validated or checked using the PP-based technique, or vice versa. Alternatively, the average of, or the results of the techniques based on PP and CM, can be calculated statistically. Many such permutations and combinations are possible in a manner compatible with the teachings of the present invention.

Side Search Methodology

Referring now to FIG. 7, the methodology of lateral placement of the flattener transducer assembly 402 is described. As discussed above, it is desirable to properly place transducer 422 directly on the blood vessel in question (eg, artery radial) before performing the optimal flattening, measurement and scaling procedures discussed above. Such proper lateral placement helps ensure a high level of coupling between the blood vessel wall and the transducer face, and in a sense helps to alleviate the loss of transfer.

As shown in Figure 7, the exemplary method 700 of the illustrated embodiment comprises first placing the flattening element 402 (and thus the pressure transducer 422) generally on the blood vessel of interest according to step 702 as described above with respect to Figure 5. The flattening element 402 is fastened within a bracelet or other apparatus such that the former is generally placed on the inner surface of the subject's wrist. It is noted that the present method provides for some degree of lateral misalignment.

Next, in step 704, the flattening level for the flattener 402 is adjusted to maintain a substantially constant pressure reading from the transducer 422. This adjustment comprises "servo control" around the designated pressure to closely maintain the constant target pressure. . This pressure is selected to provide adequate signal coupling between the artery wall and the active face of the transducer (through the interposed tissue and the coupling layer 423), while also allowing the movement of the transducer 422 (and the coupling layer 423) along the surface of the subject's skin without friction or excessive deformation of the tissue that may be painful for the subject, or cause anomalies in the measured pressure waveform.

The flattener 402 is then moved laterally along the subject's wrist to an initial position that is deviated from the blood vessel in question (step 706). For example, in one embodiment, the flattener 402 is moved towards the lateral part of the subject's wrist, closer to the radial bone (and specifically the styloid process). However, it will be recognized that other initial positions (for example, medial or otherwise) may be used. The flattener 402 is placed using a side-by-step 845 motor (see the assessment in Figure 8 below) that is coupled with the flattener 402. However, such placement can be achieved using any type of driving force, and can Perform manually if desired.

Once the flattener 402 is placed at its initial point, the pulse pressure (PP) (step 708) is monitored based on the systolic and diastolic components obtained from the pressure waveform of the transducer 422.

Next, in step 710, a lateral position scan is started using the lateral positioning motor 845, the latter dragging the flattener 402 (and pressure transducer 422) along the surface of the subject's skin while It is controlled in the sagittal direction to maintain the predetermined pressure mentioned above. In the present embodiment, a linear position scan is used; that is, constant travel speed along the surface of the wrist, although it will be appreciated that, as with the flattening scan described above, other profiles (nonlinear or otherwise) can be used. Pulse pressure is measured during the scanning of step 710, and the data is stored for analysis.

The scan rate is selected to allow a sufficient collection of pressure waveform data and calculation of the PP per unit of time, thus providing the desired level of granularity for the PP measurements. Specifically, if the scan speed is too high, only a few PP data points will be generated, and the lateral position accuracy will be degraded. On the contrary, if the scanning speed is too slow, the location of the position using the PP will be high, but the location process will be long, thus extending the time required to ultimately obtain a blood pressure measurement.

The scanning of step 710 continues until (i) a predetermined position is achieved for the flattener 402 with respect to the initial position; and / or (ii) a maximum pulse pressure is observed. Other criteria can also be used to complete the first lateral position scan. Figure 7a illustrates an exemplary profile of PP versus the lateral position obtained using method 700.

Once the side scan of step 710 is completed, a second side scan is completed in the opposite direction (step 712). As shown in Figure 7b, this second scan moves back over the first scan and records the measured PP again as a function of time and / or position. In one embodiment, the second scan works along a smaller region (i.e., smaller lateral distance) than the first scan, and at a lower speed to achieve a more precise location for the artery. Criteria are used to complete the second scan similar to those used in the first scan (step 710).

After completing the second scan (step 712), the data collected for both scans (step 714) is analyzed to determine if a maximum of authentic PP has been observed. Specifically, each data set is analyzed to determine if the maximum PP value is produced in a lateral position (determined, for example, by encoding the position of the stepper motor) corresponding to that of the other scan, within a recommended error band. If the PP maximums are well correlated, there is high confidence that one of the two maximums (or a position between them) will understand the authentic position at which a maximum PP pressure will be measured. On the contrary, if the two maxima are not well correlated, additional data collection (sweeps) may be required to resolve the ambiguity and / or more accurately locate the desired lateral position for transducer 422.

In addition to maxima that are not well correlated in terms of position, side sweep profiles with multiple local maxima and / or artifacts can be observed. As shown in Figures 7c-7d, the movement of the subject during scanning or other sources may induce noise within the profile (s), thus frustrating the identification of the position of authentic maximum. In the present embodiment, the appearance of multiple maxima or no maximum (as determined, for example, by a mathematical analysis of each interval of the scan with respect to the others) will disqualify a given side scan for consideration, and will require sweeps additional (step 716). Signal processing algorithms that can identify artifacts and maximum / minimum within pressure waveforms are well known in the art, and therefore are not further described herein.

It is also noted that a "statistical mode" of operation can be employed with respect to the method 700 described above. Specifically, a plurality of lateral position scans can be performed before performing the analysis of step 714, a corresponding (or lower) number of those sweeps being included in the analyzed data set. In this way, artifacts or noise that are present in a sweep may not be present in the next, and therefore will have a less degrading effect on the determination of the final position. Signal processing and / or statistical analysis can be performed on the resulting data if desired.

In addition, the method of Figure 7 (and the apparatus of Figure 8 below) can be configured to iteratively locate around a calculated position. For example, each lateral placement scan is analyzed at the end, and the results of the maximum location analysis are used to locate the spatial region for subsequent scanning (s). Specifically, in one embodiment, the PP data obtained from the first lateral position scan is analyzed, and the location of maximum PP is identified. Based on this information, the lateral positioning motor (in the direction of movement opposite to the original scan) is repositioned at the beginning of a position window centered around the maximum detected PP location. Then a second “mini-scan” of reduced duration is performed while the PP is measured, and subsequently the PP data is analyzed at the end of the mini-scan to identify the location of maximum PP. If desired, correlation analyzes such as those described hereinbefore may or may not be applied to determine the correlation between the maximum PP locations in each scan. This procedure can be continued if desired to more accurately locate the maximum PP location. It can also be performed periodically during continuous monitoring of blood pressure (that is, after having determined the optimum level of flattening and having applied any necessary scale adjustment of the waveform, according to Figure 5 above) if desired, to compensate for patient movement, slippage, etc. Specifically, the system can take a "rest" from the lateral placement, in which the controller causes the flattening motor 406 to remove the flattener 402 to the predetermined constant pressure level (step 704 of Figure 7), and are performed one or more side refresh sweeps.

It will be recognized that innumerable different permutations of the previous stages (i.e. compression to a desired level, lateral flatner movement 402 along the blood vessel, and maximum analysis) can be used in a manner compatible with the present invention. All these permutations and modifications of this methodology are, given the disclosure provided in this document, within the scope of those of ordinary skill in the art.

System apparatus for hemodynamic evaluation

Referring now to Figure 8, an apparatus for measuring hemodynamic properties within the blood vessel of a living subject is now described. In the illustrated embodiment, the apparatus is adapted for the measurement of blood pressure within the radial artery of a human being, although it will be recognized that other hemodynamic parameters, monitoring sites and even types of living organisms may be used in relation to the invention. in its broadest sense.

The exemplary apparatus 800 of Figure 8 essentially comprises the flattening assembly 400 of Figure 4 (which includes the element 402 and the pressure transducer 422) for measuring the blood pressure of the radial artery in a tonic manner; a digital processor 808 operatively connected to / to the pressure transducer (s) 422 (and various intermediate components) to (i) analyze the signals generated by the transducer (s);

(ii) generate control signals for the stepper motor 406 (by means of a microcontroller 811a operatively coupled to the stepper motor control circuits); and (iii) store measured and analyzed data. The motor controllers 811, processor 808, auxiliary card 823 and other components can be housed either locally with respect to the flattener 402, or alternatively in a separate independent housing configuration if desired. The pressure transducer 422 and its associated storage device 852 are optionally made detachably from the flattener 402 as described in greater detail below with respect to Figure 8a.

The pressure transducer 422, in the present embodiment, is a voltage beam transducer element that generates an electrical signal in functional relationship (for example, proportional) with respect to the pressure applied to its detection surface 421, although others may be used. technologies. The analog pressure signals generated by the pressure transducer 422 are converted into a digital form (using, for example, an ADC 809) after optionally being subjected to a low pass filter 813 and sent to the signal processor 808 for analysis. Depending on the type of analysis used, the signal processor 808 uses its program (either embedded or stored in an external storage device) to analyze the pressure signals and other related data (for example, stepper motor position according to It is determined by the position encoder 877, scaling data contained in the EEPROM 852 of the transducer by means of a signal 12C 1, etc.).

As shown in Figure 8, the apparatus 800 is also optionally equipped with a second stepper motor 845 and associated controller 811b, the second motor 845 being adapted to move the flattener assembly 402 laterally along the blood vessel ( for example, the radial artery) of the subject as described above with respect to Figure 7. The operation of the lateral positioning motor 845 and its controller 811b is substantially analogous to that of the flattening motor 406, in a manner compatible with the methodology of the figure

7.

As previously mentioned, continuous, accurate, non-invasive measurements of hemodynamic parameters (eg blood pressure) are highly desirable. For this, the apparatus 800 is designed to (i) identify the appropriate level of flattening of the subject's blood vessel and associated tissue; (ii) continually “servo control” this condition to keep the blood vessel / tissue properly diverted to perform the best possible tometric measurement; and (iii) scale the tometric measurement as needed to provide an accurate representation of intravascular pressure to the user / operator. During a flattening "sweep", the controller 811a controls the flattening motor 406 to flatten the artery (and the interposed tissue) according to a predetermined profile, such as that described with respect to Figure 5. Similarly, the extension and removal of the flattening element 402 during the last states of the algorithm (i.e., when the flattening motor 406 is removed to the optimum flattening position, and subsequent servo control around this point) using controller 811a and processor 808 .

The apparatus 800 is also configured to apply the scale adjustment methodologies discussed above with respect to Figures 5d-5i. Specifically, as mentioned with respect to Figure 5d above, the corrected pressure waveform (adjusted to scale) is derived by (i) subtracting the average pressure measured in a tonic way from “n” average pulses of each value of subsequent tometric sample pressure (a sample result of "zero mean"); (ii) multiply each “zero average” sample value derived in (i) by the derived scale factor, and add again the average average pressure value of “n” beats; and (iii) repeat the procedure every "n" beats, using a newly derived scale factor. The resulting waveform is a scaled waveform that is effectively corrected for transfer loss.

In an alternative implementation, a "stretch" calculation is performed according to equation 7 after the flattening and optimization scanning procedure is completed:

Pts = Ptin + (Pth xSIMC) (Ec. 7)

where:

Pts = "stretched" or corrected tonic pressure Pin = uncorrected tometric pressure Pth = uncorrected tonic pressure (subjected to high pass filter) SIMC = BMI stretch factor

This function effectively generates the corrected tonic pressure data by adding the uncorrected pressure data to a high-pass filter component of the uncorrected data that has been scaled by the BMI stretch factor. Based on empirical data, the BMI stretch factor in the present embodiment is set at a range of from about 0.0 and +0.6, although other values may be used.

Note that during a flattening sweep of the “stretch” calculation, the scale adjustment functionality described above is automatically deactivated (also with automatic activation feature) since no scale adjustment is required during the process of identifying the artifact in issue (for example, maximum pulse pressure point). Additionally, the user / operator is allowed to determine the value of the minimum cut-off point for the hemodynamic parameter (for example, the pressure) for the flattening scan. A default value is set at 90 mmHg, although other values can be substituted. This minimum cut-off point helps prevent the system from triggering an invalid event in a parasitic or erroneous way (for example, a “false” maximum that can occur at low pressure values due to the system configuration).

When the device 800 begins the data acquisition, a routine that calculates the high pass filter coefficients of the 4th order of the system (with a cutoff frequency of 0.1625 Hz, which is selected to eliminate any DC component) is optionally started. present in the signal). Additionally, for each data block (ie, each group of data associated with a given monitoring interval), the apparatus 800 performs a parallel calculation of high pass filter tometric data for the "stretch" calculation.

The present embodiment also includes a heartbeat detection algorithm. When a new beat is detected (based on the processing of the tometric pressure waveform), a software call is made to update the stretch factor determined by BMI. If the subject's BMI information has not yet been entered, then the system simply updates the pressure (pulse) history for future calculations.

The physical apparatus 800 of Figure 8 comprises, in the illustrated embodiment, a substantially autonomous unit having, among others, a combined pressure transducer 422 and a flattening device 400, motor controllers 811, RISC digital processor 808 with memory 817 Associated synchronous DRAM (SDRAM) and a set of instructions (including scaling tables), LED display 819, front panel input device 821, and power supply 823. In this embodiment, the 811 controllers are used to control the operation of the combined pressure / flattening transducer device, the control and scaling algorithms being implemented continuously, based on initial operator / user inputs.

For example, in one embodiment, the user input interface comprises a plurality (for example, two) of buttons arranged on the face of the device housing (not shown) and coupled with the LCD screen 879. The programming of the processor and the LCD controller are configured to visually present interactive requests to the user through the 879 screen after pressing each of the two buttons. For example, in the present context, a button is assigned as a "weight range" button, in which, when pressed, the LCD display 879 asks the user to select from a plurality of differentiated weight ranges. Similarly, the "height range" function is assigned to the other button, in which its pressing causes the user to be asked through the screen to select one of a plurality of height ranges. Once these two values have been entered, the device 800 automatically determines the PP as described above, and uses the two inputs to calculate the BMI, which then automatically relates to the PP to generate a scaling factor. Such visual presentation and control functions are within the skills of the ordinary experts in electronic techniques, and therefore are not further described herein.

In addition, a patient monitoring interface (MP) circuit 891 shown in Figure 8 can be used to act as an interface between the apparatus 800 and an external or third-party patient monitoring system. Exemplary configurations for such interfaces 891 are described in detail in the pending US patent application together with the present US 2003 141916 entitled "Apparatus and Method for Interfacing Time-Variant Signals" filed on January 29, 2002, and assigned to the assignee of this document, although other approaches and circuits may be used. The interface circuit referred to has the distinctive advantage of automatically acting as an interface with literally any type of patient monitoring system regardless of its configuration. Thus, the apparatus 800 of the present invention coupled to the aforementioned interface circuit allows doctors and other healthcare professionals to connect the apparatus to on-site monitoring equipment already available in their facilities, thus eliminating the need (and the cost) associated with a dedicated monitoring system solely for the measurement of blood pressure.

Additionally, an EEPROM 852 is physically coupled to the pressure transducer 422 as shown in Figures 8 and 8a, so that a unit unit 850 is formed that can be separated from the central apparatus 800. Details of the construction and operation of such coupled assemblies are described in detail in US Patent 6676600 entitled "Smart Physiologic Parameter Sensor and Method", filed on August 31, 2000, assigned to the assignee of this document.

Using a coupled and detachable arrangement of this type, both transducer 422 and EEPROM 852 can be easily separated and repositioned within system 800 by the operator. Referring to the scale adjustment methodologies described above in this document (for example, IMC / PP and IMC / CM), the differentiated scale adjustment intervals are advantageously correlated with the unit assembly 850 in such a way that different sets for different intervals of scale adjustment. For example, in the context of the BMI / CM method as best shown in Table 1 above, three unit 850 sets are provided, one corresponding to each Is scale index range. Therefore, EEPROM 852 of each set 850 is encoded with the appropriate scale factor (s) corresponding to that Is scale index, and is also visually encoded (eg, by color). The user / operator selects the appropriate set 850 based on the BMI / CM value (scale index) obtained from the subject to be monitored, and introduces the set 850 into the apparatus 800. The adjustment factors are recovered from the EEPROM. scale or related data present in the EEPROM 852, and are applied to the waveform not scaled (after the level of flattening, etc., they are optimized as described hereinabove) to produce an output adjusted to scale. This approach has the benefit of eliminating the introduction or selection of data in the system by the operator; the operator simply determines the scale index value (such as by nomogram or calculator), and then selects the appropriate set 750 based on the color (or the text information on the set or its package).

It will be recognized that the use of a limited number of transducer / EEPROM assemblies can also be easily applied to the IMC / PP methodology described above. For example, the entire BMI / PP interval can be divided into n = 0, 1, 2 ... differentiated intervals (either linearly or in a compressed-expanded manner), with a separate set 850 for each interval. Then the EEPROM 852 for each set will contain the scale adjustment data applicable to that interval, such scale adjustment data being for example a segment of scale adjustment function, "stretch" factor, or the like. As yet another alternative, the assemblies 850 can be encoded based solely on the BMI value, thus preventing the operator from determining the PP and calculating the BMI / PP. Many other such variants are possible, considering that they are all within the scope of the present invention.

It is also noted that the apparatus 800 described herein can be constructed in a variety of different configurations, and using a variety of different components other than those specifically described herein. The construction and operation of such an apparatus (given the description provided herein) are easily within the scope of the usual expert in the field of electronics and medical instrumentation, and are therefore not further described herein.

The computer program (s) for implementing the aforementioned hemodynamic evaluation methods using optimal flattening and scaling is also included in the apparatus 800. In an exemplary embodiment, the The computer program comprises a representation in object code ("machine") of a C ++ source code list that implements the methodology of Figures 5d-5i, either individually or in combination thereof. Although C ++ language is used for the present embodiment, it will be appreciated that other programming languages may be used, including for example VisualBasic ™, Fortran and C +. The object code representation of the source code list is compiled and can be arranged in a media storage device of the type known in computer techniques. Such media storage devices may include, without limitation, optical discs, CD ROMs, magnetic floppy disks or "hard" disks, tape disks, or even magnetic bubble memory. The computer program further comprises a graphical user interface (GUI) of the type known in programming techniques, which is operatively coupled to the display and input device of the apparatus or the central computer in which the program is executed.

As for the general structure, the program is composed of a series of subroutines or algorithms to implement the flattening and scaling methodologies described in this document based on measured parametric data provided to the central apparatus 800. Specifically, the computer program comprises a set of assembly / microcoded language instructions disposed within the embedded storage device, that is, program memory, of the digital processor or microprocessor associated with the hemodynamic measuring apparatus 800. This last embodiment provides the advantage of compactness because it eliminates the need for a separate PC or similar hardware to implement the functionality of the program. Such compactness is highly desirable in clinical and home settings, where space (and ease of operation) is scarce.

Method to provide treatment

Referring now to Figure 9, a method for providing treatment to a subject using the methods mentioned above is disclosed. As illustrated in Figure 9, the first step 902 of method 900 comprises selecting the blood vessel and the location to be monitored. For most human subjects, this will include the radial artery (monitored inside the wrist), although other locations may be used in cases where the radial artery is compromised or otherwise unavailable.

Next, in step 904, the flattening mechanism 400 is placed in the appropriate location with respect to the subject's blood vessel. Such placement can be achieved manually, that is, by the caregiver or the subject by visually aligning the transducer and the device on the inside of the wrist, by the pressure / electronic / acoustic positioning methods referred to above, or by other means. Next, the first flattening element 402 is operated according to step 906 to flatten the tissue surrounding the blood vessel to a desired level to identify an optimal position in which the effects of transfer loss and other errors associated with the tometric measurement. The previous evaluation referring to Figure 5 in this document illustrates an exemplary method for finding this optimal level of flattening.

Once the optimum flattening level for the flattening element 402 is set, the pressure waveform is measured according to step 908, and the relevant data is processed and stored as required (step 910). Such processing may include, for example, calculation of the pulse pressure (systolic minus diastolic), calculation of average pressures or average values over limited time intervals, and optional scale adjustment of the form (s) of measured pressure wave (s). Then one or more resulting outputs (for example, systolic and diastolic pressures, pulse pressure, average pressure, etc.) are generated in step 912 based on the analyzes performed in step 910. Then the relevant parts of the procedure are repeated ( step 914) if desired to provide continuous monitoring and evaluation of the subject's blood pressure.

Finally, in step 916, the "corrected" measurement of the hemodynamic parameter (for example, systolic and / or diastolic blood pressure) is used as the basis for providing treatment to the subject. For example, corrected systolic and diastolic blood pressure values are generated and presented visually or otherwise provided to the healthcare provider in real time, such as during surgery. Alternatively, such measures can be collected over an extended period of time and analyzed to detect long-term trends in the state or response of the subject's circulatory system. Pharmacological agents or other treatment cycles may be recommended based on the resulting blood pressure measurements, as is well known in medical techniques. Similarly, since the present invention provides continuous measurement of blood pressure, the effects of such pharmacological agents on the physiology of the subject can be monitored in real time.

It is noted that many variations of the methods described above can be used in a manner compatible with the present invention. Specifically, certain stages are optional and can be performed or removed as desired. Similarly, other steps (such as additional data sampling, processing, filtration, calibration or mathematical analysis, for example) can be added to the above embodiments. Additionally, the order of realization of certain stages can be exchanged, or performed in parallel (or in series) if desired. Therefore, the above embodiments are only illustrative of the broader methods of the invention disclosed herein.

The above description is the best currently contemplated way of carrying out the invention. It is not intended in any way that this description is limiting, but rather should be taken as illustrative of the general principles of the invention. The scope of the invention should be determined with reference to the claims.

Claims (35)

one.

Apparatus for measuring the pressure in a blood vessel of a living subject, the apparatus comprising a flattening element (402) comprising a sensor (422) adapted to determine the pressure associated with said blood vessel and producing signals related to the same, said flattening element being further configured to apply a level of compression to said blood vessel; and a processor operatively connected to said sensor, said processor being configured to generate an estimate of blood pressure within said vessel based at least in part on said signal and scaling data provided to the processor, said estimate being substantially representative of the actual pressure within said blood vessel, characterized in that the processor is further configured to provide scale adjustment data by selecting appropriate scale adjustment data to apply to said signals, or pressure data derived therefrom, said adjustment data being selected at scale using the body mass index (BMI) of said living subject.

2.

Apparatus according to claim 1, further adapted to place at least a part of the sensor in contact with tissue lining said blood vessel, and:

variably compress said blood vessel over time using said sensor; determine the level of compression at which there is a desired condition of the associated pulse pressure with said blood vessel based on the signals produced by said sensor; Y keeping said sensor at or near said level of compression at which said desired condition exists.

3.

Apparatus according to any of the preceding claims, wherein said scaling device is adapted to:

receive a first physiological value from said subject; receive a second physiological value from said subject; obtain said BMI based at least in part on a relationship between the first and second values; Y use said BMI to scale these signals or pressure data.

Four.

Apparatus according to claim 3, wherein said first and second physiological values comprise the weight and height of said subject, respectively.

5.

Apparatus according to claim 2, further comprising a positioning apparatus configured to vary the position of said sensor in a substantially lateral direction with respect to said blood vessel so that said desired condition of said determination is optimized.

6.

Apparatus according to claim 5, wherein said positioning apparatus is further configured to vary the position of said sensor in a substantially proximal direction with respect to said blood vessel so that said desired condition is optimized.

7.

Apparatus according to claim 6, wherein said desired condition comprises maximum pulse pressure, and at least one of said position variations comprises:

measure at least one pressure waveform during said variation action; vary the position of said sensor over a range of positions; and identify the position in which said pulse pressure is maximized for a given compression level.

8.

Apparatus according to claim 1, further comprising an apparatus for determining an average pressure within at least one pressure waveform obtained from said sensor; and wherein said scaling device applies said scaling factor to pressure values of said waveform above and below said mean.

9.

Apparatus according to claim 8, wherein said flattening assembly is further adapted to:

placing at least part of the sensor in contact with tissue that covers said blood vessel; variably compress said blood vessel over time using said sensor; determine the level of compression at which there is a desired condition of the associated pulse pressure with said blood vessel based at least in part on the signals generated by said sensor; Y keeping said sensor at or near said level of compression at which said desired condition exists.

10.

Apparatus according to claims 8 or 9, wherein said scale adjustment apparatus applies scale adjustment factors to said pressure values higher and lower than said mean by applying a positive scale adjustment factor (+) to systolic pressures greater than said mean, and a negative scale adjustment factor (-) at diastolic pressures lower than said mean.

eleven.

Apparatus according to claim 1, wherein said scale adjustment apparatus comprises a digital processor having at least one computer program running therein, said program being adapted to perform at least a part of said scale adjustment.

12.

Apparatus according to claims 1 or 2, further comprising a flattening apparatus coupled to said sensor and configured to control the position of said sensor in at least one dimension with respect to said blood vessel.

13.

Apparatus according to claim 1, further comprising:

at least one storage device associated with said sensor, said at least one storage device having said scaling data stored therein; and at least one flattening assembly adapted to divert a part of tissue close to said blood vessel.

14.

Apparatus according to claim 13, wherein said blood vessel comprises the radial artery of a human being, and said part of tissue is disposed on the wrist of said subject.

fifteen.

Apparatus according to claim 13, wherein said sensor is physically coupled to said at least one flattening assembly, and comprises at least one active surface that comes into contact with said part of said fabric, said part of tissue covering at least partially said blood vessel.

16.

Apparatus according to claim 13, further comprising a controller for controlling said at least one flattening assembly, wherein said controller and scaling apparatus comprise a single integrated circuit device (CI).

17.

Apparatus according to claim 13, further comprising at least one computer program adapted to control the level of deviation applied to said tissue part.

18.

Apparatus according to claim 17, wherein said at least one computer program is further adapted to maintain said level of deflection such that the pulse pressure associated with said blood vessel is substantially maximized.

19.

Apparatus according to claim 13, wherein said sensor and said at least one storage device comprise a substantially unitary assembly adapted for removal from said apparatus.

twenty.

Apparatus according to claim 19, wherein said at least one storage device contains scaling data adapted for use in a subject having a BMI that is within a predetermined range.

twenty-one.

Apparatus according to claim 20, wherein said unit assembly is visibly encoded to identify the range of said BMI for which it can be used.

22

Apparatus according to claim 21, wherein said visible coding comprises color coding, the unit set associated with each interval having a different color.

2. 3.

Method for measuring the pressure in a blood vessel (404) of a living subject in a tonic way, the method comprising providing a pressure transducer (422) configured to determine the pressure applied thereto in close proximity to said blood vessel; applying a level of compression to said blood vessel by said pressure transducer; and measuring at least one pressure value using said transducer; characterized in that the method further comprises:

selecting a scaling factor to apply to said at least one pressure value, said selection being made based on the body mass index (BMI) of the living subject at least one pressure value; and scaling said at least one pressure value using said selected scale adjustment factor to produce a corrected value, said corrected value being substantially representative of the actual pressure within said blood vessel.

24.

Method according to claim 23, wherein said action of applying a compression level comprises performing a flattening scan from an undercompression state of said blood vessel to an overcompression state.

25.

Method according to claim 24, wherein said flattening scan comprises at least one of: a linear variation of the position of said sensor as a function of time, or a gradual variation of the position of said sensor as a function of time.

26.

Method according to claim 24, further comprising determining a level of compression to be applied to said blood vessel, said level of compression being determined by:

obtaining at least one pressure waveform during said flattening scan; and identifying at least one artifact within said at least one waveform, said at least one artifact being associated with a desired condition.

27.

Method according to claim 26, wherein said identification of at least one artifact comprises:

analyze said at least one waveform for each beat; evaluating at least a second parameter associated with a first beat of said at least one waveform; evaluate said at least one second parameter associated with at least one other beat of said at least one waveform; Y apply at least one criterion to said beats to identify said desired pulse pressure condition.

28.

Method according to claim 27, wherein said at least a second parameter comprises the pressure amplitude, and said desired condition comprises maximum pulse pressure.

29.

Method according to claim 27, wherein said at least one other beat comprises two consecutive beats, said two consecutive beats being sequential with said first beat, said criterion comprising a difference in the pressure amplitude of a predetermined percentage.

30

Method according to claim 23, further comprising generating a scaling parameter by

(i)

 forming a ratio of said BMI with respect to a pulse pressure (PP) measured from said subject; Y

(ii)

 add or subtract a constant value from the value of that ratio.

31.

Method according to claim 30, further comprising scaling said at least one pressure value based at least in part on a scaling parameter, using said scaling parameter said BMI and said PP.

32

Method according to claim 23, further comprising generating a scaling parameter by

(i) form a ratio of said BMI with respect to a wrist circumference (CM); and scaling said at least one pressure value based at least in part on said scaling parameter.

33.

Method according to claim 23, further comprising varying said level of compression at a rate that is at least in part a function of the heart rate of said subject.

3. 4.

Method according to claim 23, further comprising:

determine said BMI of said subject; identify a relationship between said BMI and a scaling factor for said signals or pressure data measured from said blood vessel; Y use said scaling factor to scale these pressure signals or data.

35

Method according to claim 23, further comprising receiving said BMI from a user interface.